For example, a gas turbine includes a compressor, a combustor, and a turbine. Air taken in from an air inlet port is compressed by the compressor to compressed air with high-temperature and high-pressure. Fuel is supplied to the compressed air for combustion in the combustor, and the high-temperature and high-pressure combustion gas drives the turbine and a generator connected to the turbine. In this case, the turbine has a chamber in which a plurality of stator vanes and rotor blades are alternately arranged, and an output shaft to which the generator is connected is rotated and driven by driving the rotor blades with the combustion gas. The combustion gas having driven the turbine is converted into static pressure by a diffuser in an exhaust casing, and released to atmosphere.
In the combustor of the gas turbine formed in this manner, an inner tube is contained in and supported by an outer casing, and a casing is formed by connecting a combustor transition piece to an end portion of the inner tube. An air passage that supplies high-pressure air to the inner tube is formed between the outer casing and the inner tube. A pilot nozzle is arranged at the center of the inner tube, a plurality of main fuel nozzles is arranged at an inner peripheral surface of the inner tube, and a pilot burner is arranged at the periphery of the pilot nozzle.
A bypass pipe is connected to the combustor transition piece, and the bypass pipe forms a bypass passage for supplying high-pressure air to the combustor transition piece. A high-pressure flow rate adjustment valve is installed in the bypass pipe.
Accordingly, an air flow of the high-temperature and high-pressure compressed air compressed by the compressor flows into the air passage of the gas turbine combustor, and is introduced into the inner tube. In the inner tube, the compressed air and fuel injected from a fuel nozzle are mixed, and flow into the combustor transition piece as a swirl flow of an air-fuel premixture. At this time, the air-fuel mixture is ignited by the pilot burner, combusted, and generates combustion gas. At this time, a part of the combustion gas is blown into the combustor transition piece so as to be diffused to surrounding areas with a flame. Accordingly, the air-fuel premixture injected from the main fuel nozzles is ignited and combusted. The compressed air from the compressor is divided into combustion air guided to the inner tube through the air passage and bypass air guided to the combustor transition piece through the bypass pipe, by opening and closing the flow rate adjustment valve. Accordingly, the air-fuel ratio in the inner tube can be adjusted. The air-fuel ratio is reduced by opening the flow rate adjustment valve, and the air-fuel ratio is increased by closing the flow rate adjustment valve.
In the gas turbine combustor operated as described above, combustion vibrations may occur during the combustion of air-fuel mixture. The combustion vibrations cause noise and vibration during the operation of the gas turbine. In particular, in recent gas turbines, environmental effects are taken into consideration during operation, and reduction of nitrogen oxide (NOx) from flue gas has been carried out. To reduce NOx, fuel-lean combustion is often used. However, in the lean combustion, combustion tends to become unstable, thereby easily generating combustion vibrations. Accordingly, the conventional gas turbine combustors include a damping device to damp vibrations.
For example, Patent document 1 discloses a gas turbine combustor that includes the damping device. In the gas turbine combustor disclosed in Patent document 1, an acoustic damper is attached to a bypass elbow. The acoustic damper includes a holder mounted so as to hold the bypass elbow, a pair of acoustic boxes fixed at an interval from the bypass elbow, and a pair of cassettes arranged between the bypass elbow and the pair of acoustic boxes and fixed with the holder. The cassettes include a porous metal. Accordingly, low frequency vibrations resonate in the acoustic boxes including a resonance pipe in a maze shape, and the porous metals fixed to more than two locations can damp vibrations over a wider range of frequencies.
[Patent document 1] Japanese Patent Application Laid-open No. 2006-022966